The present invention is directed generally to a vehicle anti-lock brake system (“ABS”) and, more particularly to an ABS in which a single ABS electronic control unit (“ECU”) can be used with alternative ABS arrangements and configurations.
ABSs function to prevent locking of individual wheels during vehicle braking and, thus, to shorten braking distance without losing lateral traction, especially during braking on smooth surfaces. For braking of commercial vehicles, a braking medium such as compressed air is typically introduced in controlled manner into the brake cylinders in order to actuate the appropriate wheel brakes. Brake systems of the ABS type are typically equipped with modulators (solenoid valves) in the compressed air lines. Such modulators are actuated by an ABS ECU to increase, maintain or reduce brake pressure. For this purpose, each modulator is provided with an inlet and an outlet valve.
In the case of ABSs for commercial vehicles, a distinction can be made between a large number of conventional systems. For example, commercial vehicles may have one, two, three or more axles. Each axle is usually provided with two wheels, although more wheels may be provided. These wheels may or may not be equipped with sensing devices such as wheel speed sensors.
Each wheel brake may be provided with its own modulator, or, alternatively, one common modulator for each axle or for each side of the vehicle may be provided. Use of a common modulator ensures that the same brake pressure is applied to both wheels of an axle or of one side of the vehicle. In this connection, several regulation strategies are known in the art, including, for example, select-low regulation (“SL”), select-high regulation (“SH”), modified axle regulation (“MAR”) (see e.g., DE 3733801) and variable axle regulation (“VAR”) (see e.g., DE 19723323).
For commercial vehicles having three axles, one of which is a (steered) front axle and two of which are rear axles, two ABSs are common.
The first of the above-noted common ABSs is equipped with six wheel speed sensors and six brake pressure modulators. This system is known as the “6S/6M system,” based on the number of wheel speed sensors (S) and modulators (M). The 6S/6M system provides for individual regulation (“IR”), since all wheels of the vehicle can be regulated individually. Individual regulation has the advantage of a particularly short braking distance. On the other hand, a disadvantage of this “full system” is its complexity and cost.
The second common ABS for tri-axle vehicles is also equipped with six wheel speed sensors, but only four modulators. This system is therefore known as the “6S/4M system.” In the 6S/6M system, the front axle is equipped with two separate modulators providing IR, while the brake cylinders of the two rear axles are supplied jointly via only two modulators. In most cases, the common supply is of side-by-side design, meaning that the two wheels of one side of the vehicle are supplied jointly by one of the modulators. It is also possible, however, to supply the two wheels of each axle with one common axle modulator (see WABCO Brochure ABS/ASR “D”-“CAB” version 8/99, p.9). The advantage of this “partial system” for tri-axle vehicles with common supply, as compared with IR, is that two fewer modulators are needed. This system is implemented with one of the above-noted regulation strategies (e.g., SL, SH, MAR or VAR).
Heretofore, two different configurations of ABS ECUs have been standard for the foregoing two systems: an ECU with six complete regulating channels (full system) for the 6S/6M system, and an ECU with only four complete regulating channels for the 6S/4M system (partial system). A complete regulating channel comprises the components and signals between wheel speed sensor and output amplifier or end stage for the modulator of a given vehicle wheel.
The ECUs of these two ABS versions have the same outward appearance, the difference is that, to save costs, two fewer end stages are built into the 6S/4M version. Consequently, manufacture of the ECUs for the two ABS versions require parts having separate identification. This translates into higher costs for production and warehousing, especially if only limited quantities of individual versions are sold.
Furthermore, if an ECU for a 6S/4M ABS were to be mistakenly installed in a vehicle ABS equipped for a 6S/6M ABS ECU, the 6S/4M ABS ECU would recognize two superfluous modulators and signal an error if the 6S/4M ABS ECU is properly connected to the 6S/6M ABS via the associated cable harness. However, if the plug connectors for the fifth and sixth modulators are not inserted in this case (the plug and socket connector between the cable harness and ABS ECU is the same for the two systems), the 6S/4M ABS ECU would detect only four modulators and thus would erroneously recognize the installation to be valid and would deliver regulation signals (SL) unsuitable for regulated braking.
Accordingly, it is desired to provide an improved ABS ECU that is compatible with both 6S/6M and 6S/4M ABSs and eliminates the need for maintaining a large inventory of different ABS ECUs for different ABSs. It is also desired to provide an improved ABS that avoids the afore-noted disadvantages associated with the installation of an incompatible ABS ECU.